The Ammeter and the Voltmeter MCQ Quiz - Objective Question with Answer for The Ammeter and the Voltmeter - Download Free PDF

• An ammeter is originated from ampere meter
• The resistance of an ideal ammeter should be zero so that there is no voltage drop across the ammeter.
• An ideal ammeter would present no resistance to a circuit and will measure the most accurate value of current in a circuit.
• An ammeter is an instrument connected in series for measuring the electric current.

CONCEPT:

Electrical Meters and Resistance

• Electrical meters are devices used to measure electrical quantities such as current, voltage, and resistance. The resistance of these meters is an important factor in their design and functionality.
• Ammeter, milliameter, galvanometer, and voltmeter are different types of electrical meters, each with varying resistances.

EXPLANATION:

• Let's examine the given options:
  • Option 1: Ammeter
    • An ammeter is used to measure electric current. It is designed to have very low resistance so that it does not affect the current it is measuring.
  • Option 2: Milliameter
    • A milliameter is a type of ammeter that measures small currents in milliamperes. It also has very low resistance, similar to an ammeter.
  • Option 3: Galvanometer
    • A galvanometer is an instrument for detecting and measuring small electric currents. It has higher resistance compared to an ammeter and milliameter.
  • Option 4: Voltmeter
    • A voltmeter is used to measure electrical potential difference between two points. It is designed to have high resistance to minimize the current draw from the circuit being measured.

Therefore, the correct answer is option 2: Milliameter.

Explanation:

Current through ammeter = 1 A

R_net = 6Ω

V_AB = 0.5 × 4 = 2 volt

V_CD = 1 × 4 = 4 volt

Hence,

A, B & D are correct 

Concept:

A voltmeter's sensitivity is the voltage it reads per division, i.e., the voltage it measures per unit deflection of the needle.

To change the sensitivity of a voltmeter, additional resistance can be added to alter the total resistance and thus modify the scale.

For a voltmeter to read a higher voltage per division, the total resistance must be increased, as the sensitivity is inversely proportional to the total resistance.

Calculation:

Given:

The internal resistance of the voltmeter is 1000Ω.

The original sensitivity is 0.5 V/div.

The desired sensitivity is 1 V/div.

Let the required high resistance to be connected in series be Rs.

The total resistance required to double the voltage per division is:

R_total = 2 × R_v

Substituting the given value of R_v (1000Ω):

R_total = 2 × 1000Ω = 2000Ω

The total resistance is the sum of the internal resistance (R_v) and the added resistance (R_s):

R_total = R_v + R_s

2000Ω = 1000Ω + R_s

R_s = 2000Ω - 1000Ω = 1000Ω

∴ The value of the high resistance to be connected in series is 1000Ω.
Hence, the correct answer is: Option D) 1000Ω.

So, for \(I\) to increase, \(S\) should decrease, so additional \(S\) can be connected across it.

CONCEPT:

Galvanometer:

• A galvanometer is used for detecting current in an electric circuit.
• The galvanometer is the device used for detecting the presence of small currents and voltage or for measuring their magnitude.
• The galvanometer is mainly used in the bridges and potentiometer where they indicate the null deflection or zero current.
• The potentiometer is based on the premise that the current sustaining coil is kept between the magnetic field experiences a torque.

EXPLANATION:

• From the above, it is clear that the galvanometer is the instrument used for detecting the presence of electric current in a circuit. Therefore option 1^st is correct.

​Additional Information 

Difference between Ammeter and Galvanometer:

• The ammeter shows only the magnitude of the current.
• The galvanometer shows both the direction and magnitude of the current.

Explanation:

Ammeter:

•  It is a device used to measure the current in a circuit.
• It is generally connected in series in a circuit. 
• This is because the current remains the same when devices are connected in series. 
• The ideal ammeter has low resistance because the reading will change as an extra resistance is added in series. 

Additional Information

Voltmeter:  

• It is a device used for measuring the electric potential difference between two points in an electric circuit.
• It is connected in parallel across the two points to measure the voltage drop between the points.
• This is because the potential difference remains the same if devices are connected in parallel. 
• The voltmeter has high resistance because the overall resistance will not change if low resistance path is offered to the current in form of voltmeter. 

CONCEPT:

• Voltmeter: The electrical instrument which is used to measure the potential difference between two points in an electric circuit is called a voltmeter.
  • The Voltmeter is connected in parallel in an electric circuit.
• Galvanometer: It is used to detect the presence of small electric current and voltage. It is connected in series.
• Fuse: A fuse is a safety device that melts and breaks the circuit when the current exceeds a particular level and thus save the other appliances connected to the circuit.
  • It is connected in series. 
• Ammeter: The electrical instrument which is used to measure the electric current in an electric circuit is called an ammeter. 
  • An Ammeter is connected in the series combination because the current remains constant in the series combination.
  • This helps in getting an accurate reading from the instruments.

EXPLANATION:

• Since the potential difference remains constant in the parallel combination. That's why the voltmeter is connected in parallel in an electric circuit. So option 1 is correct.

The correct answer is Ohmmeter.

Key Points

• The ratio of the potential difference between the ends of a resistor to the current flowing through it is called its electrical resistance.
• It is measured in 'ohms'.
• An ohmmeter is an electrical device used to measure resistance.

Additional Information

• Ammeter -
  • It is an instrument for measuring the current flowing in a branch of a circuit.
• Voltmeter -
  • It is a measuring instrument used to measure the potential difference between any two points of a circuit.
• Galvanometer -
  • It is a kind of ammeter only.
  • It is used to detect the presence of current in a circuit.

CONCEPT:

• ​Circuit: It is a closed-loop or path which forms a network of electrical components, where electrons are able to flow. This path is made using electrical wires and is powered by a source, like a battery.
• Simple circuit: A simple circuit comprises the power source, conductors, switch, and load.
  • Cell: It is the power source
  • Load: It is also termed as the resistor. It is a light bulb that lights when the circuit is turned on.
  • Conductors: They are made of copper wires with no insulation. One end of the wire is connected the load to the power source and the other end of the wire connects the power source back to the load.
  • Switch: It is a small gap in the circuit. There are various types of switches. A switch can be used to open or close a circuit.
• Voltmeter: A voltmeter is an instrument used for measuring the electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has high resistance so that it takes a negligible current from the circuit.

EXPLANATION:

• The voltmeter is used to measure the potential difference. It is always connected in parallel across the points where the potential difference is to measure so one end of the voltmeter is connected to the point A of a resistance AB and the other end to the point Bm and also it has high resistance so that it takes a negligible current from the circuit.
• Voltmeters have high resistance, so in series, they would greatly decrease the current going to the circuit.
• Hence option 4 is correct.

CONCEPT:

• Potential difference: The amount of work done to bring a unit positive charge from one point to another is called the potential difference. 
  • Its unit is volt.
  • To flow current between two points, there should be some potential difference between them.
  • Potential difference is provided by a cell or its combination called a battery.
• Ohms Law: Potential difference at constant temperature is directly proportional to current.

V = IR

V is the potential difference between two points, I current, R is the resistance between two points.

• Resistance: The property to resist electric current is called resistance. Its unit is Ω.
• Voltmeter: The device used to measure the potential difference between two points in the circuit is called a voltmeter.

CONCEPT:

• Ammeter: It is a device used to measure current and is always connected in series with the ‘element’ through which current is to be measured.
• Voltmeter: It is a device used to measure potential difference and is always put in parallel with the ‘circuit element’ across which potential difference is to be measured

EXPLANATION:

• Conversion of galvanometer into voltmeter: A galvanometer may be converted into a voltmeter by connecting a large resistance R in series with the galvanometer. Therefore option 4 is correct.
• The equivalent resistance of the combination = G + R

Where G = resistance of galvanometer.

• If nth part of applied voltage appeared across galvanometer (i.e Vg = V/n) then required series resistance is R = (n - 1)G.

CONCEPT:

• Voltmeter: The device that is used to measure the electrical potential difference between two points in an electric circuit is called a voltmeter.
  • The voltmeter is connected in parallel with the circuit to measure the same voltage drop that occurs across it.
  • An ideal voltmeter allows all the current to pass through the circuit without any hindrance.

EXPLANATION:

• An ideal voltmeter allows all the current to pass through the circuit without any hindrance. So that reading of voltage has no error. As V =IR
• This is possible only when there is no current pass through the voltmeter in the parallel circuit.
• There is no current pass through the voltmeter only when it has infinite resistance.
• So an ideal voltmeter should have infinite resistance.

CONCEPT:

Measuring instruments are:

EXPLANATION:

• The devices connected in parallel have the same potential difference across them.
• So, in order to calculate the potential difference across a device, the voltmeter must be connected in parallel. 

CONCEPT :

• Ohm's Law: A law that states that electric current is proportional to voltage and inversely proportional to resistance. Mathematically,

V = IR

where R is the resistance, I is current, and V is the voltage across the conductor.

• In the Series circuit, the equivalent resistance is the algebraic sum of all the resistances.

Req = R1 + R2 + R3 +......  (In Series)

• And in the Parallel circuit, the reciprocal of the equivalent resistance is the algebraic sum of all the reciprocal of the resistances.

1/Req = 1/R1 + 1/R2 + 1/R3 +...... (in Parallel circuit)

• Voltage in a Parallel circuit is the same for all the branches.

CALCULATION:

We know that Voltage in a Parallel circuit is the same for all the branches.

Branch B and Branch C are parallel. So the voltage across B and C will be the same.

So V_B = V_C

On combining a parallel combination of 1.5 Ω & 3 Ω," id="MathJax-Element-1-Frame" role="presentation" style="position: relative;" tabindex="0">,, ,  the equivalent resistance

\(\frac{1}{R}=\frac{1}{1.5}+\frac{1}{3}\)

R = 1 Ω 

and the resistance of A = 1 Ω